The electronic and geometrical structure of the ground and excited states of Co, and Co. has been calculated using the density functional theory with two generalized gradient approximations for the exchange-correlation potential. The computed electron affinity Of CO2 ((5)Delta (g)) is in good agreement with experiment. For each permitted spin multiplicity, Co-2 possesses several states having close bond lengths and/or total energies. It is found that Co, possesses an antiferromagnetic singlet state which is inaccessible by excitations from the triplet states but could be reached through magnetic de-excitations.